LARGE bull sharks might be lurking in greater numbers in the murky water in the mouth of Mary River after the floods, a shark expert has warned.

Jonathan Werry, a shark research scientist with Ocean and Coast Research, said the risk of a shark attack was likely to increase in this area because of the murky water conditions and other factors which attracted bull sharks to feed in that area.

"The risk is increased during these periods," Dr Werry said.

"The bull sharks are coming in to feed."

He said while it wasn't their first preference, bull sharks were also known to inhabit man-made canals if they became accessible after floods and other land-locked bodies of water if they became accessible.

"They do move into these areas," Dr Werry said.

Queensland's shark control program manager Jeff Krause told ABC radio people should not tempt fate when it came to risking a bull shark attack by entering those waterways.

"It's their preferred environment - turbid or murky water - along the coastline and in estuaries, so we advise people, just hold off going for a swim."